Tsunade is slightly faster than Hiruzen, and vastly stronger than him, forcing him to avoid taijutsu at all costs.
Hiruzen's chakra reserves are piss-poor in comparison to Tsunade's.
Tsunade can tank everything he has, and wear him out.
The only feasible argument is genjutsu. But then again, he's featless in that.
Tsunade can't get close enough to attack Hiruzen.
The databook disagrees; she's slightly faster than him. She doesn't need to get close, anyway, he'd be smart enough to avoid taijutsu with her anyway and wear him down when his ninjutsu proves useless against her. How does Hiruzen hurt Tsunade when she took Madara's Susanoo sword straight through her with no problems?